System/browser settings to reduce motion:

Help page: https://developer.mozilla.org/en-US/docs/Web/CSS/@media/prefers-reduced-motion#user_preferences

Overriding Firefox config: in about:config create new pref: ui.prefersReducedMotion set to 1.

I gave up

Animation is no longer modified to be instant or removed completely - animation curve is modified to instantly jump to the end, but all timers are preserved.

This should reduce side effects listed below.

This script may have side effects:

• sometimes events attached to animation will not fire. I still work on this from time to time. One of workarounds is to set duration of the animation to very low value (0.001ms) - this have slight effect on performance - your benchmark scores may be bit lower.
• you may see page jumps when (auto)scrolling. This is (I think) side effect of jQuery animation jumping to the end immediately.
• dropdown fields selection may jump randomly (flicker)
• marquee/carousel/slideshow-like animations may scroll very fast using lot of resources (commenting out delays/durations adjustment will help)
• youtube cinema mode switching may not work (player width will stuck)
• google login page may stuck on greyed password field
• endomondo login page may stuck (white page, orange progress on top)
• map on mygpsfiles.com cannot be resized
• DuckDuckGo search r###lts may flicker/jump on hover
• olx.pl search r###lts may stuck on spinner

Because of this, new js-only version is available now https://greasyfork.org/scripts/40529-animalqueryjs Issues may also been fixed in new Firefox releases (66 looks promising)

This script is developed and used in Firefox, Violentmonkey